Grinder and method for controlled edge break production

ABSTRACT

A robust grinding assembly is provided for grinding cooling holes in a dovetail groove by offsetting the drive shaft of the cutting assembly with respect to the center axis of the bar in which it is housed, whereby a larger sized collet can be accommodated.

BACKGROUND OF THE INVENTION

Referring to FIG. 1, during the manufacture of a turbine wheel/rotor/disk 10, an axisymmetric groove 12 is turned radially into the underside of the rim. A subsequent linear machining (broach) operation creates the axial dovetail slot shape 14. These two features intersect creating a hole 16 at the bottom of the slot 14. The edge of the hole created is sharp, so it is necessary to grind the edge so that it is rounded.

Historically, the sharp edge was ground free-hand with a pencil grinder. Later, tooling was developed, as shown in field repair document FRD-2003-1002 from GE Energy Services, the disclosure of which is incorporated herein by this reference, and as schematically illustrated in FIG. 2. That tooling is comprised of a 90° head cutting tool 20 seated in a special tool holder (bar) 22. The 90° head tool is a standard tool for 1/16 inch shank cutters offered by NSK America Corp. The special tool holder (bar) 22 was developed to receive the standard tool for controlled edge break production.

Referring to FIG. 2, the special tool holder or bar 22 has a cross-bore 24 defined therethrough transverse to the longitudinal axis, and a side open slot 26. The cradled tool 20 is held, axially aligned with the tool bar 22 and with the 90° head extending through the cross-bore 24, by a suitable fastener plate 28 secured to bar 22. Thus, the cutting bit (not shown in FIG. 2) is loaded and protrudes from the side of the bar 22 opposite the slotted side. The cutting bit is shaped like a router bit and the tool is used analogously on a manifold surface as a router is used on a planar surface, such as a table top.

BRIEF DESCRIPTION OF THE INVENTION

A more robust assembly is provided according to example embodiments of the invention by offsetting the drive shaft of the cutting assembly with respect to the center axis of the bar in which it is housed, whereby a larger sized collet and bearing can be accommodated.

Thus, the invention may be embodied in a grinding tool comprising: a main body; a drive shaft bore defined along at least a part of the length of said main body, said drive shaft bore having an axis disposed in parallel to a longitudinal center axis of said main body and laterally offset therefrom; a cross bore defined generally transverse to said longitudinal axis at least part way through said main body to intersect said drive shaft passage; a drive shaft disposed to extend through said drive shaft passage of said main body; and a cross head assembly disposed in said cross bore for selectively receiving and holding a cutter and for being driven to rotate said cutter by said drive shaft.

The invention may also be embodied in a method of grinding an edge of a cooling hole of a dovetail groove, comprising: providing a tool including a main body, a drive shaft bore defined along at least a part of the length of said main body, said drive shaft bore having an axis disposed in parallel to a longitudinal center axis of said main body and laterally offset therefrom, a cross bore defined generally transverse to said longitudinal axis at least part way through said main body to intersect said drive shaft passage, a drive shaft disposed to extend through said drive shaft passage of said main body, and a cross head assembly disposed in said cross bore for selectively receiving and holding a cutter and for being driven to rotate the cutter by said drive shaft; securing a cutter to said cross head assembly; operatively coupling a torque motor to said drive shaft; inserting said main body into a dovetail groove so that the main body is disposed in a base portion of the dovetail groove and the cutter is disposed adjacent the edge to be ground; actuating the motor; and displacing the cutter about and along the edge to grind the same.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of this invention, will be more completely understood and appreciated by careful study of the following more detailed description of the presently preferred exemplary embodiments of the invention taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a perspective view of a cooling slot surface in a dovetail groove;

FIG. 2 is a schematic, exploded view, partly in cross section, showing assembly of a conventional grinding tool to a tool holder bar;

FIG. 3 is an elevational view illustrating a bench tool assembly according to an example embodiment of the invention;

FIG. 4 is an elevational view illustrating a field tool assembly according to another example embodiment of the invention; and

FIG. 5 is an enlarged view of the grinding tool portion of FIGS. 3 and 4.

DETAILED DESCRIPTION OF THE INVENTION

As noted above, the 90° head cutting tool 20 conventionally provided for grinding the wheel cooling slot was a standard tool for 1/16″ shank cutters. While more controlled than a pencil grinder, the conventional tool assembly lacks robustness with the primary failure modes being broken shanks, looseness in the cradle due to wear, and poor surface finish.

As understood from a consideration of FIG. 1, the diameter of the conventional tool bar 22 was limited by the diameter of the dovetail base 18 in which it is disposed for routing about the sharp edge of hole 16. The inventors recognized that the axially aligned tool and bar of the conventional assembly and the limited diameter of the dovetail base limited the tool to a 1/16″ collet. The 1/16″ tool has small drive shaft bearings and small cutter support bearings, plus a weak 1/16″ collet. The inventors further recognized that a ⅛″ collet tool would be more rigid yielding a more robust assembly. The associated bigger bearings mean less heat generation and consequently less wear. A bigger support bearing also yields a more rigid tool. Furthermore, a ⅛″ collet would be substantially stronger than the prior 1/16″ collet.

As mentioned, the size of the assembly is necessarily limited by the diameter at the base of the dovetail, but the inventors recognized that a ⅛ tool could be accommodated in the required package envelope (defined by the base 18 of the dovetail groove) by offsetting the drive shaft. Moreover, exercising careful choice of bearings and assembly sequence gives strength and compactness. In this regard, in illustrated example embodiments, the cross head components load from the cutter side and are retained by a snap ring.

Furthermore, to provide better tool stiffness, reduce component parts and increase robustness of the assembly, according to example embodiments of the invention, the grinding tool has been integrated into an elongated bar, thereby eliminating a two-part grinding tool plus bar assembly previously provided. This eliminates the prior problem of looseness in the tool bar cradle due to wear. With better tool stiffness and a stronger cutter shank, the material removal process can be better controlled with reduced cutter chatter and gouging. A larger shank cutter also yields longer tool life.

Two example embodiments of the integrated grinder and bar are illustrated herein. One example embodiment 30 may be used during manufacture (bench) whereas another embodiment 130 is proposed for use in the field. In these example embodiments, the grinding tool assembly 32, which is an integration of a grinder and a bar, is the same but bearing handles 34, 134 differ. The example bench tool 30 is depicted in FIG. 3, the example field tool 130 is depicted in FIG. 4, and FIG. 5 is an enlarged illustration of the grinding tool assembly 32 common to the respective tools.

As understood from FIGS. 3 and 4, a torque motor 36 as provided for the conventional grinding tool is advantageously provided for driving the cutter head. Furthermore, as in the illustrated examples, a speed reducer 38 can be interposed between the torque motor 36 and the grinding tool assembly 32. As illustrated in FIG. 5, the grinding tool assembly 32 includes a 90° offset head main body 40 for accommodating the cutter and its drive shaft. To accommodate a ⅛″ shank cutter 42, the 90° offset head main body 40 has a drive shaft receiving passage 44 with a center line D that is offset to a center line M of the main body 40. In this regard, it is understood that the diameter of the offset head (outside diameter) is limited by the diameter of the base 18 of the dovetail groove 14 in which the cutter 42 is to be operated. Component parts such as the speed reducer 38 and torque motor 36, which are disposed outside of the dovetail groove 16, are not so limited. Thus, offsetting the passage 44 for the drive shaft housing 46 and drive shaft 48 therein with respect to a center axis M of the main body 40 allows it to accommodate the ⅛″ shank cutter 42, which is not only thicker than but has a longer shaft than the 1/16″ shank cutter (not shown).

The component parts of the cutter assembly for receiving and driving the ⅛″ cutter are also larger. In this regard, not only is the collet larger, as a ⅛″ collet rather than a 1/16″ collet, but the additional space afforded by the offset of the drive shaft 48 allows the maximum size ball bearing 50 close to the cutter 42 which lowers heat generation and increases rigidity. In the illustrated example embodiment, the cutting assembly includes, from the side opposite the cutting face, a wave disk spring 54, a ball bearing 52, a standard NSK drive gear 56, a ball bearing 50 (as noted above) and a retaining snap ring 58. In this regard, careful choice is made in bearings and assembly sequence to give strength and compactness. Further in this regard, the cross head components load from the cutter side and are retained by snap ring 58, whereas in the conventional assembly, the cross head component parts are loaded from the side opposite the cutting face.

The larger cutter assembly also means a larger drive shaft 48 and hence bigger bearings 50, 52 than for a 1/16″ cutter. Bigger bearings means less heat generation which equates with less wear.

In the illustrated example embodiments, a jam nut 64 and control arm 66 are further provided at one end of the grinding tool main body. These component parts are optional for the bench tool 30 but in the illustrated embodiment, one such control arm is shown interposed between the speed reducer 38 and the main body 40. The field tool 130 is illustrated as having a control arm on either end of the grinding tool. The control arm(s) facilitate operation of the tool in both axial and rotational motion relative to the centerline M of the tool.

Attached to the distal end of the main body 40 of the bench tool 30 is a bearing handle 34 to facilitate controlled, two handed manipulation of the grinding tool assembly 32 with respect to the cooling hole being ground. In the illustrated example embodiment, the bearing handle 34 is attached to the distal end of the main body 40 by engaging and threading complimentary threaded components defined at the interface 68 thereof. The bearing handle could be integrally included as a part of the main body, but a detachable bearing handle allows the handle type to be changed as deemed necessary or desirable, and depending on whether the tool is for bench or field use. For example, an interchangeable bearing handle allows for the use of an alternate handle material, e.g., plastic, aluminum, titanium, carbon fiber, etc., to lower the overall weight of the tool and reduce ergonomic stress. The bearing handle can also optionally be knurled as at 76 in FIG. 4. In this regard, knurling is a matter of personal preference. Further, the bearing handle can be equipped with straps or braces or other enabling technologies or attachment to a robotic manipulator can be made. This amenability to customization and technology application is another advantage of a detachable, interchangeable handle.

As illustrated in FIG. 4, the field tool embodiment incorporates a modified bearing handle 134. In the illustrated example, the bearing handle 134 for field use has a bore 70 defined therethrough through which a threaded anchor rod 72, e.g. a socket head cap screw, is disposed. Providing a separate anchor rod uncouples the control handle 66 orientation from the bearing handle 76 uniting functionality. The retaining rod in the illustrated example embodiment is coupled to the main body via a threaded attachment at their junction 168. Further, in the illustrated example, an O-ring 74 is interposed between the rod and the bore wall of the bearing handle 134 to reduce the likelihood of the fastener falling out during assembly/disassembly. Finally, a control arm 66 and jam nut 64 are assembled to the free end of the bearing handle 134. In this regard, using two control arms enhance stability and ergonomic effectiveness. Alternate methods of control arm attachment (not shown) such as twist locks can be applied in situations incompatible with the jam nut strategy.

Thus it will be understood that the tool described herein is an electrically driven, right angle drive grinder utilizing e.g. a ⅛″ collet size for rigidity. The packaging has been optimized for access to confined spaces. It can be used with fluted cutters and burrs. It is applicable to both OEM (original equipment manufacture) and field use (assembled rotor) to produce a smooth, continuous blend of turbine wheel air cooing slots. With higher tool stiffness and a stronger cutter shank, the material removal process can be better controlled with reduced cutter chatter and gouging. A larger shank cutter also yields longer tool life.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 

1. A grinding tool comprising: a main body; a drive shaft passage defined from a proximal end of said main body along at least a part of the length of said main body, said drive shaft passage having an axis disposed in parallel to a longitudinal center axis of said main body and laterally offset therefrom; a cross bore defined generally transverse to said longitudinal axis at least part way through said main body to intersect said drive shaft passage; a drive shaft disposed to extend through said drive shaft passage of said main body; a cross head assembly disposed in said cross bore for selectively receiving and holding a cutter and for being driven to rotate said cutter by said drive shaft; and a bearing handle detachably secured to a distal end of said main body, said bearing handle having a free distal end, wherein said drive shaft passage is laterally offset from the longitudinal center axis of the main body in a direction away from a projecting direction of said cutter out of said main body.
 2. A grinding tool comprising: a main body; a drive shaft passage defined along at least a part of the length of said main body, said drive shaft passage having an axis disposed in parallel to a longitudinal center axis of said main body and laterally offset therefrom; a cross bore defined generally transverse to said longitudinal axis at least part way through said main body to intersect said drive shaft passage; a drive shaft disposed to extend through said drive shaft passage of said main body; and a cross head assembly disposed in said cross bore for selectively receiving and holding a cutter and for being driven to rotate said cutter by said drive shaft; wherein said drive shaft passage is laterally offset from the longitudinal center axis of the main body in a direction away from a projecting direction of said cutter out of said main body, and wherein said cross head assembly includes a ⅛″ collet for receiving a ⅛″ cutter.
 3. A grinding tool as in claim 1, further comprising a torque motor operatively coupled to said drive shaft.
 4. A grinding tool as in claim 3, wherein a speed reducer is interposed between said torque motor and said drive shaft.
 5. A grinding tool as in claim 3, wherein said torque motor is axially aligned with said drive shaft and axially offset with respect to the center axis of said main body.
 6. A grinding tool as in claim 2, wherein said drive shaft passage is defined from a proximal end of the main body along at least a part of the length of the main body, and further comprising a bearing handle detachably secured to a distal end of said main body, said bearing handle having a free distal end.
 7. A grinding tool comprising: a main body; a drive shaft passage defined from a proximal end of said main body along at least a part of the length of said main body, said drive shaft passage having an axis disposed in parallel to a longitudinal center axis of said main body and laterally offset therefrom; a cross bore defined generally transverse to said longitudinal axis at least part way through said main body to intersect said drive shaft passage; a drive shaft disposed to extend through said drive shaft passage of said main body; a cross head assembly disposed in said cross bore for selectively receiving and holding a cutter and for being driven to rotate said cutter by said drive shaft; and wherein said drive shaft passage is defined from a proximal end of the main body along at least a portion of the length of the main body and further comprising a bearing handle detachably secured to a distal end of said main body, wherein said bearing handle is selectively operatively coupled to said main body so as to be axially aligned with the center axis thereof.
 8. A grinding tool as in claim 1, wherein said bearing handle has a bore defined therethrough for selectively receiving an attachment rod and wherein said attachment rod is selectively coupled to said main body to secure said bearing handle thereto.
 9. A grinding tool as in claim 8, wherein said attachment rod is coupled with said main body through the utilization of a threaded fastener.
 10. A method of grinding an edge of a cooling hole of a dovetail groove, comprising: providing a tool including a main body, a drive shaft passage defined along at least a part of the length of said main body, said drive shaft passage having an axis disposed in parallel to a longitudinal center axis of said main body and laterally offset therefrom, a cross bore defined generally transverse to said longitudinal axis at least part way through said main body to intersect said drive shaft passage, a drive shaft disposed to extend through said drive shaft passage of said main body, and a cross head assembly disposed in said cross bore for selectively receiving and holding a cutter and for being driven to rotate the cutter by said drive shaft; securing a cutter to said cross head assembly; operatively coupling a torque motor to said drive shaft; inserting said main body into a dovetail groove so that the main body is disposed in a base portion of the dovetail groove and the cutter is disposed adjacent the edge to be ground; actuating the motor; and displacing the cutter about and along the edge to grind the same.
 11. A method as in claim 10, wherein said cross head assembly includes a ⅛″ collet and wherein said securing comprises securing ⅛″ cutter to said cross head assembly.
 12. A method as in claim 10, wherein a speed reducer is selectively interposed between said torque motor and said drive shaft.
 13. A method as in claim 10, wherein said torque motor is axially aligned with said drive shaft and axially offset with respect to the center axis of said main body.
 14. A method as in claim 10, wherein said torque motor is attached to said drive shaft at a first, proximal end of said main body and further comprising: providing a bearing handle and attaching the bearing handle to a second, distal end of the tool main body.
 15. A method as in claim 14, wherein said bearing handle is attached to said main body so as to be axially aligned with the center axis thereof.
 16. A method as in claim 14, wherein said bearing handle has a bore defined therethrough for selectively receiving an attachment rod and wherein said attachment rod is coupled to said main body.
 17. A method as in claim 16, wherein said attachment rod is threaded to said main body.
 18. A grinding tool as in claim 7, wherein said bearing handle has a bore defined therethrough for selectively receiving an attachment rod and wherein said attachment rod is selectively coupled to said main body to secure said bearing handle thereto.
 19. A grinding tool as in claim 18, wherein said attachment rod is coupled with said main body through the utilization of a threaded fastener.
 20. A grinding tool as in claim 6, wherein said bearing handle is selectively operatively coupled to said main body so as to be axially aligned with the center axis thereof. 